Conventionally, in a device for controlling an automatic transmission configured to execute slip lockup control by which a slip amount of a lockup clutch is brought to a target slip amount, when a rate of change in a required load for an engine is greater than or equal to a predetermined threshold value, the target slip amount is increased at a predetermined rate of increase, and then the increased target slip amount is decreased at a predetermined rate of decrease. At this time, the predetermined rate of decrease is set to decrease, as the operating condition when the rate of change in the required load has reached or exceeded the predetermined threshold value approaches an operating condition in which a rate of increase in a rotational speed on the automatic-transmission side of a torque converter with respect to an increase in the required load is low. Such a slip lockup control device is well known and set forth in Patent document 1, for example.